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Title: LECTURE 14: Hormones, Biological Clocks,


1
Psy 137 Behavioral Endocrinology Lecture 6
Biological Rhythms
Website http//mentor.lscf.ucsb.edu/course/summer
/psyc137/
2
Why Should Behavioral Endocrinologists be
Interested in Biological Clocks?
  • Timing of many motivated behaviors modulated by
    hormones is critical.
  • Parental care
  • Sexual behaviors
  • Territoriality
  • Locomotor activities
  • Food and water intake
  • Torpor
  • Hibernation
  • Timing of many hormone-receptor interactions is
    critical.
  • Estrogen/Progresterone/Estrus cycles
  • Insulin/Food intake
  • Prolactin/oxytocin/Nursing behaviors
  • Glucocorticoid/stress responses

3
Chronobiology
  • Scientific study of biological clocks and their
    associated rhythms
  • Also called Biochronometry
  • Began in the early 1960s
  • Had to counteract the dogma of constant
    homeostasis in biology and medicine

4
Chrono-terminology
  • Borrowed terms and concepts extensively from
    engineering disciplines to describe biological
    clocks and associated rhythms.
  • Rhythm A recurrent event that is characterized
    by its period, frequency, amplitude, and phase.
  • Period The length of time required to complete
    one cycle of the rhythm in question For
    instance, the amount of time required to go from
    peak to peak or trough to trough.
  • Frequency Computed as the number of completed
  • cycles per unit of time For example, 2
    cycles per day.
  • Amplitude The amount of change above and below
  • the average value i.e. the distance of the
    peak or nadir
  • from the average.
  • Phase Represents a point on the rhythm relative
    to
  • some objective time point during the cycle

5
Components of Biological Rhythms
  • Rhythm a recurrent event
  • Period a cycle
  • Frequency cycles per unit of time
  • Amplitude change above/below the average value
  • Phase a point on the rhythm relative to some
    objective time point during the cycle

6
Exogenous vs Endogenous Control of Biological
Clocks
  • Some behavioral rhythms have been recognized
    since ancient times, but they have generally been
    attributed to exogenous (outside the organism)
    factors that elicit behavioral responses (e.g.
    dawn-dusk, seasons) which are called zeitgebers
    (german for time giver).
  • Recent evidence indicates that endogenous (inside
    the organism) timing mechanisms mediate many of
    the observed rhythms in physiology and behavior.
  • How is it determined whether a rhythm is the
    result of exogenous factors or an endogenous
    clock?
  • Isolation experiments (a.k.a. constant
    conditions)

7
Jean Jacques dOrtous de Mairan found that the
tensionrelaxation pattern of a heliotropic
plant persisted when isolated from exogenous
factors.
8
Examples of Mammalian Rhythms
These rhythms are highly synchronized under
normal conditions. Under constant conditions
(i.e. no external cues) they persist but become
desynchronized indicated they are generated
independently.
9
Recent Evidence that Biological Clocks are
Endogenous
  • Animals maintained in constant conditions aboard
    a spacecraft orbiting far above the earth, and
    presumably away from subtle geophysical cues,
    display biological rhythms with periods/amplitude
    similar to those observed on earth.
  • Animals maintained in adjacent, but individual,
    cages in the absence of environmental cues
    display biological rhythms with slightly
    different periods, suggesting that they are not
    being driven by the same subtle geophysical cue
  • The period (and phase) of the biological rhythms
    of one individual can be transferred to another
    individual by means of tissue transplants

10
COMPARISON OF BIOLOGICAL RHYTHMS
  • Many biological rhythms persist in constant
    conditions and approximate geophysical cues
  • Circadian, Revolution of planet 24 h bio
    22-26 h
  • Circatidal, Tides 12.4 h bio 11-14 h
  • Circalunar, Phases of the moon 29.5 days bio
    26-32 d
  • Circannual, Seasons of the year 365.25 d bio
    300-400 d
  • Some rhythms persist in constant conditions, but
    do not correspond to any known geophysical cue
  • Ultradian shorter than circadian rhythms
  • Infradian longer than circadian rhythms

11
Types of Biological Clocks and Rhythms
LH Secretion in Female Ground Squirrels
12
Experiments Measuring Circadian Rhythms
Free-running rhythm (endogenous timing)
-activity rhythms are generated endogenously but
respond to light as a zeitgeber ENTRAINMENT.
13
Usefulness of biological clocks
  • Synchronizing the internal physiological and
    biochemical processes of animals
  • To promote efficient functioning
  • E.g. sleep-wake patterns sleep is not just
    period of low activity, but rather, an active
    biological state in which many processes are
    increased, including brain activity which is
    about the same as when a person is awake and
    relaxed.
  • Synchronizing the activites of animals with their
    environments (including social)
  • To prepare for predictable events (e.g., winter,
    night, etc.)
  • e.g. anticipation/predicting high food
    availability can allow animal to minimize
    dangerous activity (i.e. going to food site) and
    maximize advantageous activity (i.e. getting the
    food).
  • e.g. sexual exhaustion in male rats after
    prolonged mating rat takes 4 days to recover
    sexual motivation which matches female
    reproductive (estrous) cycle.

14
Rhythm Entrainment
Exposure to light can change onset of biological
rhythm as a function subjective time of day.
Subjective Day Subjective Night
Photononresponsive Photoresponsive
15
Rhythm Entrainment
Giving bright light pulses at different phases of
the rhythm produces variable shifts (0 4) in
endogenous rhythm. -this results in entrainment
across days.
Phase Response Curve
16
General Characteristics of Biological Clocks and
Rhythms
  • Biological clocks are found at every level of
    organization within an organism.
  • Single-celled organisms possess circadian rhythms
    so the machinery necessary to generate a rhythm
    must exist at the level of individual cells.
  • So, in multi-cellular organisms, does every cell
    possess its own biological clock?
  • Perhaps, but in multi-cellular organisms, it
    appears as if these individual biological clocks
    have been organized into some sort of
    hierarchical fashion with feedback imposed from
    above.
  • E.g., cells taken from hamster adrenals and
    maintained in culture will free-run at different
    rates. In the intact hamster, they free-run at
    the same rate.

17
General Characteristics of Biological Clocks and
Rhythms
  • Inherited
  • When mutant animals with free-running circadian
    rhythms gt 25 hrs are mated with each other, their
    offspring tend to have longer free-running
    periods than the offspring of mutants with
    free-running rhythms lt 23 hrs (and vice versa)

18
General Characteristics of Biological Clocks and
Rhythms
  • Temperature independence
  • activities or events that change body temperature
    don't significantly alter circadian clocks
  • otherwise there would be speed-ups and slow-downs
    and eventually all resemblance to a 24 hr period
    would be lost

19
General Characteristics of Biological Clocks and
Rhythms
  • Relatively resistant to the influence of
    chemicals
  • If not, the food consumed would constantly be
    altering biological clocks.
  • A few pharmacological manipulations have been
    shown, however, to affect clocks
  • Protein synthesis inhibitors
  • Alcohol (EtOH)
  • Lithium
  • Heavy water (deuterium)

20
General Characteristics of Biological Clocks and
Rhythms
  • Independence from behavioral feedback
  • Suppose a hamster housed in DD is expresses a
    24.25 h cycle of wheel running onset.
  • The hamster's wheel is locked for 10 days and hen
    it is unlocked.
  • What time will the hamster begin to run?
  • 2 predictions
  • 1) 15 min after last time-- suggesting that the
    clock suspended time-keeping while the rhythm of
    wheel running activity was not being expressed
  • 2) 150 min after last time suggesting that the
    clock continued to run even in the absence of
    behavioral feedback. Prediction 2 is the correct
    answer.

21
General Characteristics of Biological Clocks and
Rhythms
  • Entrainment is limited to specific ranges
  • A circadian rhythm can be entrained to a 23 h day
    by providing 11.5 h of light and 11.5 h of dark
    (same for 12.5 h light/12.5 h dark).
  • However, 10 h light and 10 h dark does not result
    in entrainment to a 20 hr day
  • Instead, results in free-running with sporadic
    entrainment attained at irregular intervals.
  • In hamsters, wheel running can be entrained to
    the following range 18-26 hrs.

22
Master clocks
  • Circadian clocks have been isolated after
    demonstrating that lesions eliminate circadian
    rhythms
  • Eyes of amphibians
  • Pineal glands of fish, reptiles, and birds
  • Suprachiasmatic nuclei (SCN) of the anterior
    hypothalamus in mammals
  • Slices from the SCN maintain circadian rhythms of
    electrical activity
  • SCN transplants cause recipient's rhythm to match
    that of donor
  • Environmental light entrains oscillations of SCN

23
Time Keeping in the SCN
  • Individual cells in SCN are capable of generating
    circadian rhythms via mRNA-protein interactions.
  • Cells are coupled by GAP JUNCTIONS.

24
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25
Effect of SCN Lesions
NOTE this is constant conditions animal can
still entrain to a light-dark cycle
26
SCN Transplant
27
Input to clock
light--gteyes (photoreceptors)--gtretinohypothalamic
tract--gtSCN
28
Biological clock circuit
29
Biological Rhythms Affect Hormones
30
Output from clock There are many but one has
been extensively studied in mammals
SCN--gtPVN--gtMFB--gtSCG--gtPineal pathway (where
neural information is transduced into a hormonal
message)
31
Dual Regulation of Sleep
  • Body needs sleep long-term deprivation
    death homeostatic component
  • Tiredness is not a direct function of lack of
    sleep
  • pulling the all-nighter results in progressive
    decreased alertness with a temporary rebound in
    the morning this rebound diminishes with
    prolonged deprivation.
  • Thus, there appears to be circadian and
    homeostatic components to sleep-wake cycles.

32
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33
Biological Rhythms Affect Physiology
34
Biological Rhythms in Motivation
  • Meal-time hunger not proportional to food
    deprivation.
  • Food entrainment independent of light
    entrainment and SCN.

L
D
Start Food Entrainment 3 h during L
Activity preceding food presentation
35
Hormones Affect Biological Rhythms
  • Hamsters start running 5-10 min after dark.
  • This statement is true of males but only
    partially true for females.
  • Every 4th night (coincident with estrus), females
    show a spontaneous phase advance in their
    activity onset (called scalloping).
  • Possibly functions as a means to increase chance
    of meeting a mate.
  • Scalloping is abolished by ovariectomy.
  • Estradiol treatment of free-running,
    ovariectomized hamsters reduces the period of
    activity onset

36
Hormones Affect Biological Rhythms
  • Other sex steroids also modulate CRs
  • Progesterone lengthens the period of circadian
    rhythms possibly by counteracting the effects of
    estradiol
  • Androgens also affect circadian rhythms.
  • Castration lengthens and androgen replacement
    restores the period of free-running locomotor
    rhythms in male mice
  • Hypophysectomy shortens tau
  • Thyroidectomy shortens tau

37
Are there different clocks for rhythms of
different lengths or are longer rhythms simply
the result of the multiplication of shorter
rhythms?
Relation between rhythms of different periods.
  • e.g., is the 4-day (96 h) estrous cycle of a
    hamster the result of a 4-day clock cycling once
    or a 1-day clock cycling 4 times?
  • Evaluated in studies of free-running rhythms in
    female hamsters.
  • Phase shifts of entrainment were accompanied by
    proportionate shifts in estrous cycle (light-
    dark cycle changed to 25 h, then estrous cycle
    changed to 100 h-- if reduced to 20 h, then
    estrous cycle switched to 80 h)

38
Circannual hibernation rhythms in 5 ground
squirrels.
YEAR
39
Photoperiod
  • Day length or the amount of light per day.

In Winter I get up at night, And dress by yellow
candle-light, In Summer, quite the other way, I
have to go to bed by day. --Robert Louis
Stevenson, 1885 A Childs Garden of Verses
  • Photoperiod changes across seasons
  • How does this impact biological rhythms?
  • Do biological clocks predict this change?

40
Photoperiodism
  • Photoperiodism has evolved in virtually all taxa
    of plants and animals that experience seasonal
    changes in their habitats.
  • Among vertebrate animals, photoperiodism is
    linked to a number of seasonal adaptations,
    including reproductive, metabolic, immunological,
    and morphological adaptations to cope with
    seasonal changes in ambient conditions.

41
Photoperiodism
  • Although the precise mechanisms underlying
    photoperiodism differ among taxa, individuals
    that respond to day length can precisely, and
    reliably, ascertain the time of year with just
    two bits of data
  • (1) the length of the daily photoperiod
  • (2) whether day lengths are increasing or
    decreasing.

42
Non-Tropical Animals May Evoke a Suite of
Seasonal Adaptations to Increase the Odds of
Survival and Reproductive Success
  • The initial demonstration of photoperiod
    regulating mammalian reproduction was reported
    for European field voles, Microtus agrestis by
    Baker and Ranson in 1932
  • Currently, the role of photoperiod in mediating
    seasonal adaptations has been documented for
    hundreds of vertebrate species.

43
  • Syrian, or golden, hamsters (Mesocricetus
    auratus) represent the most common mammalian
    model used in laboratory investigations of
    photoperiodism.
  • Hamsters, in common with most small mammals, are
    long-day breeders.
  • Gestation is relatively brief in these animals
    mating, pregnancy, and lactation occur during the
    long days of late spring and early summer.

44
Seasonal breeding in hamsters
Critical Photoperiod
45
Reproductive Regression
Decreased Testis Size Decreased Steroid
Production
4
3
Serum Testosterone (ng/ml)
2
1
0
Long Days
Short Days
46
Reproductive Regression
Decreased Testis Size Decreased Sperm Production
Short-Day Testis
Long-Day Testis
47
What Is the Meaning of Reproductive Regression?
  • Cessation of spermatogenesis
  • Cessation of steroidogenesis
  • Cessation of androgen-dependent traits
  • Including behavior

48
Variation in Reproductive Response to Short Days
in the Lab
  • Prairie Voles (Microtus ochrogaster)

49
Variation in Reproductive Response to Short Days
in the Lab
  • Deer Mice (Peromyscus maniculatus)

50
Seasonal Aggression in Red Deer
RUT
Aggression
T
HIGH
Antler growth
LOW
51
Human behavior also varies on an annual basis
52
Human disease and mortality also varies on an
annual basis
Death from Cardiovascular Diseases Peak in the
Winter
53
Seasonal Affective Disorder (SAD)
  • Winter depression
  • Depressed affect, lethargy, loss of libido,
    hypersomnia, excessive weight gain, carbohydrate
    cravings, anxiety, and inability to concentrate
    or focus
  • Ends in the summer
  • Frequently diagnosed as Bipolar II depression
    or Atypical Bipolar Disorder
  • Prevalence 1-10 with higher in higher
    latitudes
  • Sex difference 3.5x higher in women than men
    (also linked during postmenstrual period)
  • May result from improper entrainment as
    shortening of day length leads to early melatonin
    secretion.
  • Treatment has included litium, antidepressants,
    or estrogen and more recently light (1500 lux)
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